Data generation method, data reproduction method, data generation device and data reproduction device

ABSTRACT

A data generation method is for generating video data that covers a second luminance dynamic range wider than a first luminance dynamic range and has reproduction compatibility with a first device that does not support reproduction of video having the second luminance dynamic range and supports reproduction of video having the first luminance dynamic range, and includes: generating a video signal to be included in the video data using a second OETF; storing, into VUI in the video data, first transfer function information for identifying a first OETF to be referred to by the first device when the first device decodes the video data; and storing, into SEI in the video data, second transfer function information for identifying a second OETF to be referred to by a second device supporting reproduction of video having the second luminance dynamic range when the second device decodes the video data.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. continuation of application Ser. No. 15/611,168, filed onJun. 1, 2017, which is a U.S. continuation application of PCTInternational Patent Application Number PCT/JP2015/005894 filed on Nov.27, 2015, claiming the benefit of priority of U.S. Provisional PatentApplication No. 62/087,035 filed on Dec. 3, 2014 and Japanese PatentApplication Number 2015-219859 filed on Nov. 9, 2015, the entirecontents of which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to data generation methods, datareproduction methods, data generation devices, and data reproductiondevices.

2. Description of the Related Art

As a technique for generating, encoding, and multiplexing video, thereare the techniques disclosed in non-patent literature (NPL) 1: ITU-TH.265 “High efficiency video coding”, October, 2014, NPL 2:Recommendation ITU-R BT.709-5 (April 2002) “Parameter values for theHDTV standards for production and international programme exchange”, andNPL 3: Recommendation ITU-R BT.2020-1 (June 2014) “Parameter values forultra-high definition television systems for production andinternational programme exchange”.

SUMMARY

For such video data generation, new methods have always been devised,and there is a demand for backward compatibility with existing devices.

Thus, an object of the present disclosure is to provide a datageneration method, a data reproduction method, a data generation device,or a data reproduction device with backward compatibility.

In order to achieve the aforementioned object, the data generationmethod according to one aspect of the present disclosure is a datageneration method for generating video data that covers a secondluminance dynamic range wider than a first luminance dynamic range andhas reproduction compatibility with a first device that does not supportreproduction of video having the second luminance dynamic range andsupports reproduction of video having the first luminance dynamic range,and the data generation method includes: generating a video signal to beincluded in the video data using a second opto-electrical transferfunction (OETF) to be referred to by a second device when the seconddevice decodes the video data, the second device supporting reproductionof video having the second luminance dynamic range; storing, into videousability information (VUI) in the video data, first transfer functioninformation for identifying a first OETF to be referred to by the firstdevice when the first device decodes the video data; and storing, intosupplemental enhancement information (SEI) in the video data, secondtransfer function information for identifying the second OETF.

Furthermore, the data reproduction method according to one aspect of thepresent disclosure is a data reproduction method for reproducing videodata that covers a second luminance dynamic range wider than a firstluminance dynamic range and has reproduction compatibility with a firstdevice that does not support reproduction of video having the secondluminance dynamic range and supports reproduction of video having thefirst luminance dynamic range, the video data including: video usabilityinformation (VUI) storing first transfer function information foridentifying a first opto-electrical transfer function (OETF) to bereferred to by the first device when the first device decodes the videodata; and supplemental enhancement information (SEI) storing secondtransfer function information for identifying a second OETF to bereferred to by a second device when the second device decodes the videodata, the second device supporting reproduction of video having thesecond luminance dynamic range, and the data reproduction methodincludes: obtaining the second transfer function information included inthe SEI; and reproducing a video signal included in the video data byreferring to the second OETF identified in the second transfer functioninformation obtained.

Note that these general and specific aspects may be implemented using asystem, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a compact disc read-onlymemory (CD-ROM), or any combination of systems, methods, integratedcircuits, computer programs, or recording media.

The present disclosure can provide a data generation method, a datareproduction method, a data generation device, or a data reproductiondevice with backward compatibility.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 illustrates a configuration of a system according to anembodiment;

FIG. 2 illustrates one example of an OETF according to an embodiment;

FIG. 3 illustrates a configuration example of a VUI according to anembodiment;

FIG. 4 illustrates an example of an OETF according to an embodiment;

FIG. 5 illustrates an example of extension for OETFs according to anembodiment;

FIG. 6 illustrates a configuration example of an SEI message accordingto an embodiment;

FIG. 7 illustrates a configuration example of an SEI message accordingto an embodiment;

FIG. 8 illustrates a configuration example of an SPS according to anembodiment;

FIG. 9 illustrates a configuration example of a hybrid descriptoraccording to an embodiment;

FIG. 10 illustrates a configuration example of a hybrid descriptoraccording to an embodiment;

FIG. 11 illustrates a configuration example of an HEVC descriptoraccording to an embodiment;

FIG. 12 illustrates a stream and an operation of a data reproductiondevice according to an embodiment;

FIG. 13 is a flowchart illustrating an operation of a data generationdevice according to an embodiment; and

FIG. 14 is a flowchart illustrating an operation of a data reproductiondevice according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT Underlying Knowledge FormingBasis of the Present Disclosure

The high dynamic range (HDR) has been gaining attention as a schemecovering a luminance range with an increased maximum luminance value inorder to represent bright light such as mirror-reflected light, whichcannot be represented using current TV signals, with brightness closerto its actual brightness while maintaining dark grayscale values ofexisting video. Specifically, the scheme covering the luminance rangesupported by the existing TV signals is called the standard dynamicrange (SDR) and has the maximum luminance value of 100 nit, and the HDRis expected to have an increased maximum luminance value of at least1,000 nit.

It is desired that video data covering such an HDR be reproducible evenby an existing reproduction device that supports only the SDR. In otherwords, there is a demand for video data that is reproducible as HDRvideo by a reproduction device supporting the HDR and reproducible asSDR video by a reproduction device supporting the SDR.

The data generation method according to one aspect of the presentdisclosure is a data generation method for generating video data thatcovers a second luminance dynamic range wider than a first luminancedynamic range and has reproduction compatibility with a first devicethat does not support reproduction of video having the second luminancedynamic range and supports reproduction of video having the firstluminance dynamic range, and the data generation method includes:generating a video signal to be included in the video data using asecond opto-electrical transfer function (OETF) to be referred to by asecond device when the second device decodes the video data, the seconddevice supporting reproduction of video having the second luminancedynamic range; storing, into video usability information (VUI) in thevideo data, first transfer function information for identifying a firstOETF to be referred to by the first device when the first device decodesthe video data; and storing, into supplemental enhancement information(SEI) in the video data, second transfer function information foridentifying the second OETF.

Accordingly, a device that only supports reproduction of video havingthe first luminance dynamic range can reproduce video data using thefirst transfer function information, and a device that supportsreproduction of video having the second luminance dynamic range canreproduce video data using the second transfer function information.Thus, in the data generation method, video data having backwardcompatibility can be generated.

For example, the data generation method may further include storing,into a descriptor of a multiplexing layer, hybrid information indicatingwhether or not the video data is video data covering the secondluminance dynamic range.

Accordingly, in the data reproduction device that reproduces video data,switching of reproduction schemes can be prepared in advance using thehybrid information in the multiplexing layer. This allows smoothswitching of the reproduction schemes in the data reproduction device.

For example, the first OETF may be an OETF defined by a linear term ofluminance of the video data in a first range of the luminance of thevideo data and defined by an exponential term of the luminance of thevideo data in a second range of the luminance of the video data which isgreater than the first range.

For example, the second OETF may be an OETF defined by a linear term ofluminance of the video data in a third range of the luminance of thevideo data, defined by an exponential term of the luminance of the videodata in a fourth range of the luminance of the video data which isgreater than the third range, and defined by a logarithmic term of theluminance of the video data in a fifth range of the luminance of thevideo data which is greater than the fourth range.

For example, the first OETF may be an OETF defined by an exponentialterm of luminance of the video data.

For example, the second OETF may be an OETF defined by an exponentialterm of luminance of the video data in a sixth range of the luminance ofthe video data and defined by a logarithmic term of the luminance of thevideo data in a seventh range of the luminance of the video data whichis greater than the sixth range.

For example, the first OETF may be an OETF defined in one of BT. 709 andBT. 2020, and the second OETF may be a hybrid gamma OETF.

For example, the data generation method may further include storing,into the SEI, dynamic range increase information indicating a differencebetween a luminance dynamic range of the video data and the firstluminance dynamic range.

For example, the data generation method may further include storing,into the SEI, maximum average picture level information indicating ahighest average luminance value among average luminance values of allpictures included in a video sequence.

Furthermore, the data reproduction method according to one aspect of thepresent disclosure is a data reproduction method for reproducing videodata that covers a second luminance dynamic range wider than a firstluminance dynamic range and has reproduction compatibility with a firstdevice that does not support reproduction of video having the secondluminance dynamic range and supports reproduction of video having thefirst luminance dynamic range, the video data including: video usabilityinformation (VUI) storing first transfer function information foridentifying a first opto-electrical transfer function (OETF) to bereferred to by the first device when the first device decodes the videodata; and supplemental enhancement information (SEI) storing secondtransfer function information for identifying a second OETF to bereferred to by a second device when the second device decodes the videodata, the second device supporting reproduction of video having thesecond luminance dynamic range, and the data reproduction methodincludes: obtaining the second transfer function information included inthe SEI; and reproducing a video signal included in the video data byreferring to the second OETF identified in the second transfer functioninformation obtained.

Accordingly, in the data reproduction method, video data having backwardcompatibility can be reproduced.

For example, the video data may further include hybrid informationindicating whether or not the video data is video data covering thesecond luminance dynamic range, the hybrid information being stored in adescriptor of a multiplexing layer, and the data reproduction method mayfurther include: obtaining the hybrid information from the video data;preparing for switching between the reproduction of the video having thefirst luminance dynamic range and the reproduction of the video havingthe second luminance dynamic range, based on the hybrid informationobtained; and switching the reproduction of the video having the firstluminance dynamic range and the reproduction of the video having thesecond luminance dynamic range at a timing of a change in a videosequence.

Accordingly, switching of reproduction schemes can be prepared inadvance using the hybrid information in the multiplexing layer. Thisallows smooth switching of the reproduction schemes.

For example, the first OETF may be an OETF defined by a linear term ofluminance of the video data in a first range of the luminance of thevideo data and defined by an exponential term of the luminance of thevideo data in a second range of the luminance of the video data which isgreater than the first range.

For example, the second OETF may be an OETF defined by a linear term ofluminance of the video data in a third range of the luminance of thevideo data, defined by an exponential term of the luminance of the videodata in a fourth range of the luminance of the video data which isgreater than the third range, and defined by a logarithmic term of theluminance of the video data in a fifth range of the luminance of thevideo data which is greater than the fourth range.

For example, the first OETF may be an OETF defined by an exponentialterm of luminance of the video data.

For example, the second OETF may be an OETF defined by an exponentialterm of luminance of the video data in a sixth range of the luminance ofthe video data and defined by a logarithmic term of the luminance of thevideo data in a seventh range of the luminance of the video data whichis greater than the sixth range.

For example, the first OETF may be an OETF defined in one of BT. 709 andBT. 2020, and the second OETF may be a hybrid gamma OETF.

For example, the data reproduction method may further include obtaining,from the SEI, dynamic range increase information indicating a differencebetween a luminance dynamic range of the video data and the firstluminance dynamic range.

For example, the data reproduction method may further include obtaining,from the SEI, maximum average picture level information indicating ahighest average luminance value among average luminance values of allpictures included in a video sequence.

The data generation device according to one aspect of the presentdisclosure is a data generation device which generates video data thatcovers a second luminance dynamic range wider than a first luminancedynamic range and has reproduction compatibility with a first devicethat does not support reproduction of video having the second luminancedynamic range and supports reproduction of video having the firstluminance dynamic range, and the data generation device includes: agenerator that generates a video signal to be included in the video datausing a second opto-electrical transfer function (OETF) to be referredto by a second device when the second device decodes the video data, thesecond device supporting reproduction of video having the secondluminance dynamic range; a first storage that stores, into videousability information (VUI) in the video data, first transfer functioninformation for identifying a first OETF to be referred to by the firstdevice when the first device decodes the video data; and a secondstorage that stores, into supplemental enhancement information (SEI) inthe video data, second transfer function information for identifying thesecond OETF.

Accordingly, a device that only supports reproduction of video havingthe first luminance dynamic range can reproduce video data using thefirst transfer function information, and a device that supportsreproduction of video having the second luminance dynamic range canreproduce video data using the second transfer function information.Thus, the data generation device can generate video data having backwardcompatibility.

The data reproduction device according to one aspect of the presentdisclosure is a data reproduction device which reproduces video datathat covers a second luminance dynamic range wider than a firstluminance dynamic range and has reproduction compatibility with a firstdevice that does not support reproduction of video having the secondluminance dynamic range and supports reproduction of video having thefirst luminance dynamic range, the video data including: video usabilityinformation (VUI) storing first transfer function information foridentifying a first opto-electrical transfer function (OETF) to bereferred to by the first device when the first device decodes the videodata; and supplemental enhancement information (SEI) storing secondtransfer function information for identifying a second OETF to bereferred to by a second device when the second device decodes the videodata, the second device supporting reproduction of video having thesecond luminance dynamic range, and the data reproduction deviceincludes: an obtainer that obtains the second transfer functioninformation included in the SEI; and a reproducer that reproduces avideo signal included in the video data by referring to the second OETFidentified in the second transfer function information obtained.

Accordingly, the data reproduction device can reproduce video datahaving backward compatibility.

Note that these general and specific aspects may be implemented using asystem, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a compact disc read-onlymemory (CD-ROM), or any combination of systems, methods, integratedcircuits, computer programs, or recording media.

Hereinafter, an embodiment will be specifically described with referenceto the drawings.

Note that each embodiment described below shows a specific example ofthe present disclosure. The numerical values, shapes, materials,structural elements, the arrangement and connection of the structuralelements, steps, the processing order of the steps etc. shown in thefollowing embodiment are mere examples, and are not intended to limitthe scope of the present disclosure. Furthermore, among the structuralelements in the following embodiment, structural elements not recited inthe independent claims indicating the broadest concepts of the presentdisclosure are described as arbitrary structural elements.

Although detailed descriptions of terms, data configuration, andprocessing, etc., may be omitted below, specific examples thereof arebased on the descriptions in NPL 1, NPL2, and NPL 3, for example.

First, the configuration of a system according to the present embodimentwill be described. FIG. 1 is a block diagram illustrating theconfiguration of the system according to the present embodiment. Thesystem illustrated in FIG. 1 includes data generation device 110 anddata reproduction device 120.

Data generation device 110 generates video data that covers a secondluminance dynamic range (for example, the HDR) wider than a firstluminance dynamic range (for example, the SDR) and has reproductioncompatibility with a first device that does not support reproduction ofvideo having the second luminance dynamic range and supportsreproduction of video having the first luminance dynamic range.

Data generation device 110 include video signal generator 111, encoder112, and multiplexer 113.

Image signal generator 111 converts a luminance value of a source imagecovering the HDR into a code value using an opto-electrical transferfunction (OETF). The OETF is a function for converting the luminancevalue of the source image into the code value, as illustrated in FIG. 2.Specifically, video signal generator 111 uses an SDR-compatible HDROETF. This will be described in detail later. Note that “luminance”herein is not limited to the weighted sum of RGB components and may bethe intensity of each of the RGB components, may be the degree ofbrightness of light, or may be the intensity of light.

Encoder 112 generates a video elementary stream by encoding the obtainedcode values according to a video coding standard such as the highefficiency video coding (HEVC). Multiplexer 113 generates a transportstream (for example, a DVB transport stream) by multiplexing videoelementary streams.

The generated transport stream is transmitted to data reproductiondevice 120 by broadcast waves or the like, for example. Note that anexample in which the broadcast waves are used will be described herein,but a network or the like may be used for transmission, or a recordingmedium such as a Blu-ray Disc (BD) may be used for transmission.

Data reproduction device 120 generates the video data generated by datageneration device 110. Data reproduction device 120 includesdemultiplexer 121, decoder 122, and reproducer 123.

Demultiplexer 121 generates a video elementary stream by demultiplexingthe video data (the transport stream). Decoder 122 generates codesvalues by decoding the obtained video elementary stream according to avideo coding standard such as the HEVC.

Reproducer 123 reconstructs video by converting the obtained code valuesinto luminance values using an electro-optical transfer function (EOTF)corresponding to the OETF stated above. The EOTF is the inverse functionwhich reverses the OETF and is used for converting the code values intothe luminance values. The obtained video is displayed on a display,etc., included in data reproduction device 120 or connected to datareproduction device 120.

Signalling of the transfer function (OETF) according to the presentembodiment will be described below.

The transfer function is signalled using transfer_characteristics withinvideo usability information (VUI) included in a sequence parameter set(SPS) in the HEVC and AVC video coding standards.

The OETF alone is signalled, and the EOTF is not signalled.

FIG. 3 illustrates the syntax of a VUI parameter. As illustrated in FIG.3, the VUI includes first transfer function information(transfer_characteristics). FIG. 4 is a table indicating the semanticsof transfer_characteristics. Values 1 and 14 are assigned to SDR OETFssupported by digital video broadcasting (DVB) ultra HD (UHD) phase 1receivers.

As described in NPL 1 and the like, transfer_characteristics indicatesthe opto-electrical voltage characteristics (the opto-electricaltransfer characteristics) of the source image.

Note that signalling means including, in a transfer signal, a signal foridentifying desired information or a signal indicating such informationitself so that the receiver side can obtain the desired information. Forexample, in the example in FIG. 3 and FIG. 4, transfer_characteristicsfor identifying the OETF is included in the transfer signal, and thereceiver side identifies the OETF on the basis of the receivedtransfer_characteristics.

An example of extension for new OETFs according to the presentembodiment will be described below.

The HEVC and AVC standards have reserved values for further extension.Thus, the reserved values can be assigned to SDR-compatible HDR OETFs(hereinafter referred to as hybrid OETFs). For example, as illustratedin FIG. 5, the hybrid OETFs are assigned to values 18 to 20 which arethe reserved values.

In this case, however, a legacy data reproduction device (receiver) thatdoes not support the HDR is not capable of recognizing the new valuesand recognizes them as the reserved values. Thus, there is the problemthat when a new value is used for the hybrid OETF, it is not possible toprovide the backward compatibility. The hybrid OETF is, for example, anOETF including a part expressed as a power of luminance and a partexpressed as a logarithm of luminance, such as a BBC hybrid gamma OETF.

In the present embodiment, the value of the first transfer functioninformation (transfer_characteristics) is set to 1 (BT.709) or 14(BT.2020) as in an existing SDR.

Furthermore, in order to identify the hybrid OETF, the second transferfunction information (HDR_transfer_characteristic) is signalledseparately from the first transfer function information. Thus, in thedata reproduction device that does not support the HDR, the OETF for SDRcan be identified using the first transfer function information(transfer_characteristics), while, in the data reproduction device thatsupports the HDR, the OETF for HDR can be identified using the secondtransfer function information.

The second transfer function information (HDR_transfer_characteristic)is used for signalling of the OETF for HDR. Specifically, the OETF forHDR has compatibility with the OETF for SDR identified using the firsttransfer function information (transfer_characteristics).

For example, the second transfer function information(HDR_transfer_characteristic) indicates any of the three hybrid OETFsindicated in FIG. 5. Note that the second transfer function informationmay be information indicating whether or not to use the hybrid OETF. Thenumber of selectable hybrid OETFs may be any number greater than orequal to one.

As illustrated in FIG. 2, the characteristics of the hybrid OETFsubstantially match the characteristics of the SDR OETF in a lowluminance range. Specifically, in the low luminance range, the luminanceof video reproduced using the hybrid OETF from the video signalsgenerated using the hybrid OETF and the luminance of video reproducedusing the SDR OETF from the video signals generated using the hybridOETF are almost the same. Thus, it is possible to reduce the differencein luminance value between when the video is reproduced by an HDR deviceand when the video is reproduced by an SDR device, and therefore videothat is less likely to provide a feeling of discomfort can be reproducedeven when the video is reproduced using the SDR OETF.

Methods of storing the second transfer function information will bedescribed below. The methods are roughly classified as a method in whichthe second transfer function information is stored into a video codinglayer and a method in which the second transfer function information isstored into a multiplexing layer.

First, the method in which the second transfer function information isstored into the video coding layer will be described.

FIG. 6 illustrates the syntax of an HDR hybrid gamma SEI message(hereinafter referred to as a hybrid SEI message) according to thepresent embodiment. As illustrated in FIG. 6, the second transferfunction information (HDR_transfer_characteristic) is included in thehybrid SEI message.

The hybrid SEI message is present only in an IRAP NAL unit or anI-picture and is valid for the remainder of a coded video sequence.

Note that the hybrid SEI message may be a prefix or a suffix SEImessage.

The presence of this SEI message may be made mandatory in applicationstandardization bodies when HDR_transfer_characteristic is apredetermined fixed value.

Furthermore, as illustrated in FIG. 7, the hybrid SEI message mayinclude, in addition to the second transfer function information statedabove or instead of the second transfer function information, dynamicrange increase information (dynamic_range_increase) and maximum averagepicture level information (maximum_average_picture_level).

The dynamic range increase information (dynamic_range_increase) is usedto calculate coefficient k and has value 0, 1, or 2 only. Coefficient kindicates a difference from dynamic range SDR and is determinedaccording to the following Expression 1. Specifically, coefficient kindicates a scaling factor for the dynamic range of current video withrespect to dynamic range SDR.k=2×dynamic_range_increase+4  (Expression 1)The maximum average picture level information(maximum_average_picture_level) indicates the highest average picturelevel among all the pictures included in a video sequence. The averagepicture level means the average value of pixel luminance expressed inpercentage of the maximum luminance.

Thus, the use of the dynamic range increase information and the maximumaverage picture level information allows the difference from the SDR tobe set within an arbitrary range.

The presence of this SEI message may be made mandatory in applicationstandardization bodies when k is a predetermined fixed value. Forexample, k is equal to 4 for DVB, and k is equal to 8 for BDA.

FIG. 8 illustrates the configuration of an extended SPS. As illustratedin FIG. 8, the dynamic range increase information(dynamic_range_increase) and the maximum average picture levelinformation (maximum_average_picture_level) may be included in the SPS.

Next, the method in which the second transfer function information isstored into the multiplexing layer will be described.

FIG. 9 illustrates the configuration of a hybrid descriptor(HDR_hybrid_gamma_descriptor) which is a new descriptor at the MPEG2-TSlevel according to the present embodiment.

As illustrated in FIG. 9, the hybrid descriptor includes a hybrid OETFflag (HDR_hybrid_gamma_OETF_flag) and the second transfer functioninformation (HDR_transfer_characteristic).

The hybrid OETF flag (HDR_hybrid_gamma_OETF_flag) indicates whether ornot the content is HDR coded using the hybrid OETF. For example, whenthe hybrid OETF flag is 1, the content is HDR coded using the hybridOETF.

Note that the hybrid OETF flag is not always necessary, and it may bepossible to use only the second transfer function information.

The hybrid descriptor is stored into at least one of a program map table(PMT) specified by the MPEG, a service description table (SDT) specifiedby the DVB in the DVB-SI standard, and an event information table (EIT)specified by the DVB in the DVB-SI standard.

The PMT indicates the PID of a TS packet in which an image, audio, orthe like is stored. By obtaining the PID for a desired image, audio, orthe like from the PMT, the data reproduction device can extract the TSpacket for the desired image or audio.

The SDT indicates the name of a channel (a service), the type of the EITsent through each channel, digital copy control information, and thelike.

The EIT indicates information related to a program, such as the title,the broadcast date and time, and the broadcast content of the program.

When the hybrid descriptor is included in the PMT, the hybrid descriptoris applied to the video elementary stream only. In this case, however, abroadcaster needs to control modification of the PMT, and thismodification may be difficult.

When the hybrid descriptor is included in the SDT, the content of thehybrid descriptor is not updated often. Thus, the SDT is preferred whenthe content of the hybrid descriptor is applied to the whole service.

When the hybrid descriptor is included in the EIT, it is advantageousthat the content of the hybrid descriptor can be changed on an eventbasis.

FIG. 10 illustrates another configuration example of the hybriddescriptor according to the present embodiment. As illustrated in FIG.10, the hybrid descriptor may include, in addition to the secondtransfer function information stated above or instead of the secondtransfer function information, dynamic range increase information(dynamic_range_increase) and maximum average picture level information(maximum_average_picture_level).

FIG. 11 illustrates the configuration of an HEVC descriptor(HEVC_descriptor) according to the present embodiment. The HEVCdescriptor is a descriptor at the MPEG2-TS level. As illustrated in FIG.11, the reserved values of the HEVC descriptor are replaced with ahybrid coded flag (hdr_hybrid_gamma_coded_content_flag) and dynamicrange increase information (dynamic_range_increase). Note that thehybrid coded flag is the same as or similar to the hybrid OETF flag(HDR_hybrid_gamma_OETF_flag) described above. Furthermore, otherinformation described above (the second transfer function informationand the maximum average picture level information) may be included inthe HEVC descriptor.

The same or like extension may be applied to an AVC descriptor(AVC_video_descriptor).

The hybrid descriptor (HDR_hybrid_gamma_descriptor) described above maybe combined with signalling of the OETF to the video elementary stream(the HDR hybrid gamma SEI message). This allows smooth switching ofparameters in the data reproduction device.

Hereinafter, this operation will be described in detail. FIG. 12illustrates the configuration of the stream and the operation of thedata reproduction device.

Transmission of the hybrid descriptor (HDR_hybrid_gamma_descriptor)including the hybrid OETF flag (HDR_hybrid_gamma_OETF_flag) startsslightly before an actual change. The data reproduction device thatreceived this hybrid OETF flag prepares for the change between the SDRand the HDR.

An end of sequence (EOS) indicating the end of a video sequence isinserted into the video elementary stream in order that the parameterchange becomes active. The hybrid SEI message adapted to the lastsignalled hybrid descriptor may be or may not be stored at a randomaccess point (RAP) following the EOS.

The data reproduction device detects whether or not the EOS and thehybrid SEI message are present and makes a change according to thedetection result.

In the example illustrated in FIG. 12, the data reproduction deviceobtains the hybrid descriptor containing HDR_hybrid_gamma_OETF_flag=0 inthe HDR operating state. This allows the data reproduction device tostart preparing for switching operations from the HDR to the SDR. Next,the data reproduction device switches the HDR to the SDR at the timingwhen the EOS is obtained. The hybrid SEI message is not present within aSDR video elementary stream, and thus the data reproduction device doesnot obtain the hybrid SEI message.

Next, the data reproduction device obtains the hybrid descriptorcontaining HDR_hybrid_gamma_OETF_flag=1 in the SDR operating state. Thisallows the data reproduction device to start preparing for switchingoperations from the SDR to the HDR. Next, the data reproduction deviceswitches the SDR to the HDR at the timing when the EOS is obtained.

Hereinafter, the operations of data generation device 110 and datareproduction device 120 based on the above description will bedescribed.

FIG. 13 is a flowchart of an operation of data generation device 110according to the present embodiment. Data generation device 110generates HDR video data having reproduction compatibility with thefirst device that does not support reproduction of HDR video andsupports reproduction of SDR video.

First, video signal generator 111 generates a video signal by convertinga luminance value of a source image into a code value using the secondOETF (S101). Next, encoder 112 generates a video elementary stream byencoding the video signal. At this time, encoder 112 stores, into theVUI in the video data (the video elementary stream), the first transferfunction information for identifying the first OETF to be referred to bythe first device supporting only the SDR when the first devicereproduces the video data. Furthermore, the second transfer functioninformation for identifying the second OETF to be referred to by thesecond device supporting the HDR when the second device decodes thevideo data is stored into the SEI in the video data (S102).

The VUI and the SEI belong to the video coding layer. The first OETF is,for example, the OETF defined in BT. 709 or BT. 2020, and the secondOETF is, for example, a BBC hybrid gamma OETF.

Furthermore, encoder 112 may store, into the SEI, dynamic range increaseinformation indicating a difference between the luminance dynamic rangeof the video data and luminance dynamic range SDR. Moreover, encoder 112may store, into the SEI, maximum average picture level informationindicating the highest average luminance value among the averageluminance values of all the pictures included in the video sequence.

Next, multiplexer 113 generates a transport stream by multiplexing videoelementary stream data. At this time, multiplexer 113 stores, into thehybrid descriptor of the multiplexing layer, hybrid information (ahybrid OETF flag) indicating whether or not the video data is HDR videodata (S103).

Note that although the example in which the hybrid descriptor includesat least the hybrid OETF flag is illustrated in FIG. 12, the hybriddescriptor may further include the second transfer function information,the dynamic range increase information, or the maximum average picturelevel information.

Likewise, it is sufficient that the hybrid SEI message include at leastone of the hybrid OETF flag, the second transfer function information,the dynamic range increase information, and the maximum average picturelevel information.

Furthermore, although each of the hybrid OETF flag and the secondtransfer function information is stated as individual information in theabove description, the second transfer function information may be usedinstead of the hybrid OETF flag. This means that it is not necessary touse the hybrid OETF flag. For example, whether or not the video data isthe HDR video data (whether or not to use the hybrid OETF) can besignalled according to whether or not the second transfer functioninformation is included in the video data. Alternatively, whether or notthe video data is the HDR video data may be signalled according towhether the second transfer function information indicates the hybridOETF or the SDR OETF.

Note that the example in which the second transfer function informationindicates the hybrid OETF is described above, but when HDR video and SDRvideo are mixed in video data, as illustrated in FIG. 12, the secondtransfer function information may indicate the SDR OETF for the SDRvideo as well. Accordingly, the data reproduction device supporting theHDR may always refer to the second transfer function informationregardless of whether the video data has the SDR or the HDR. In otherwords, said data reproduction device does not need to refer to the firsttransfer function information. This allows the process of the datareproduction device to be simplified.

FIG. 14 is a flowchart of an operation of data reproduction device 120according to the present embodiment. Data reproduction device 120reproduces HDR video data having reproduction compatibility with thefirst device that does not support reproduction of HDR video andsupports reproduction of SDR video. This video data is the video datagenerated by data generation device 110, for example.

First, demultiplexer 121 generates a video elementary stream bydemultiplexing the video data (the transport stream). At this time,demultiplexer 121 obtains hybrid information (for example, the hybridOETF flag) from the hybrid descriptor of the video data (S121). Notethat demultiplexer 121 may further obtain at least one of the dynamicrange increase information and the maximum average picture levelinformation from the hybrid descriptor.

Next, data reproduction device 120 prepares for switching betweenreproduction of SDR video and reproduction of HDR video on the basis ofthe obtained hybrid information (S122).

Next, decoder 122 generates a video signal (a code value) by decodingthe video elementary stream. When the last hybrid OETF flag indicatesthe use of the hybrid OETF, decoder 122 obtains the second transferfunction information included in the hybrid SEI within the videoelementary stream (S123). Note that decoder 122 may further obtain atleast one of the dynamic range increase information and the maximumaverage picture level information from the hybrid SEI.

Reproducer 123 reproduces a video signal included in the video data byreferring to the second OETF identified in the obtained second transferfunction information (S124). Furthermore, reproducer 123 switchesreproduction of SDR video and reproduction of HDR video at the timing ofa change in the video sequence. Specifically, reproducer 123 reproducesdata following the EOS by the scheme after the change. When the dynamicrange increase information or the maximum average picture levelinformation is obtained, this information is used for the reproduction.

Note that when the last hybrid OETF flag indicates that the hybrid OETFhas not been used, decoder 122 obtains the first transfer functioninformation included in the VUI within the video elementary stream inStep S123. In Step S124, reproducer 123 reproduces a video signalincluded in the video data by referring to the second OETF identified inthe obtained first transfer function information. Note that as describedabove, when the second transfer function information selectivelyindicates the first OETF or the second OETF, decoder 122 may alwaysobtain the second transfer function information, and reproducer 123 mayrefer to the first OETF or the second OETF indicated in the secondtransfer function information.

As described above, in addition to the first transfer functioninformation which is stored into the VUI, the second transfer functioninformation is stored into the SEI message in the present embodiment.This makes it possible to implement HDR coding in which the hybrid OETFsuch as the BBC hybrid gamma OETF is used.

Specifically, whether the content is HDR coded using the hybrid OETF canbe indicated through signalling to the multiplexing layer using adescriptor.

Furthermore, the combination of a new SEI message and a new descriptorallows the data reproduction device to smoothly switch between the HDRand the SDR.

The first OETF may be the function determined according to Expression 2below.

[Math.  1] $\begin{matrix}{V = \left\{ \begin{matrix}{\alpha\;{L\left( {0 \leq L < \beta} \right)}} \\{{\gamma\; L^{\delta}} - {\rho\left( {\beta \leq L \leq 1} \right)}}\end{matrix} \right.} & \left( {{Expression}\mspace{14mu} 2} \right)\end{matrix}$

In the expression, L is the luminance of an image and is standardized as0<L<1 at a reference white level, V is a numerical value correspondingto an electric signal, and α, β, γ, δ, and ρ are each a constant andspecific numerical examples thereof are α=4.5, β=0.018, γ=1.099, δ=0.45,and ρ=0.099.

In other words, as represented by Expression 2, the first OETF may be anOETF defined by a linear term of the luminance of video data in a firstrange of the luminance of the video data and defined by an exponentialterm of the luminance of the video data in a second range of theluminance of the video data greater than the first range.

Furthermore, the first OETF may be the function represented byExpression 3 below.

[Math.  2] $\begin{matrix}{E^{\prime} = \left\{ \begin{matrix}{\alpha\;{E\left( {0 \leq E < \beta} \right)}} \\{{\gamma\; L^{\delta}} - {\left( {\gamma - 1} \right)\left( {\beta \leq E \leq 1} \right)}}\end{matrix} \right.} & \left( {{Expression}\mspace{14mu} 3} \right)\end{matrix}$

In this expression, L is the luminance of an image and defined as 0<L<1,E is a numerical value corresponding to the voltage standardized at areference white level and is proportional to the absolute lightintensity detected in reference camera color channels RGB, resulting inE′ being a non-linear signal, and α, β, γ, δ, and ρ are each a constantand specific numerical examples thereof are α=4.5, δ=0.018 (for 10-bitsystem) or 0.0181 (for 12-bit system), γ=1.099 (for 10-bit system) or1.0993 (for 12-bit system), δ=0.45, and ρ=0.099.

Furthermore, the second OETF may be the function determined according toExpression 4 below, and in this OETF, a conversion function is definedby a logarithmic term in the range of high luminance.

[Math.  3] $\begin{matrix}{V = \left\{ \begin{matrix}{\alpha\;{L\left( {0 \leq L < \beta} \right)}} \\{{\gamma\; L^{\delta}} - {\left( {\gamma - 1} \right)\left( {\beta \leq L \leq \mu} \right)}} \\{{\eta\;{\ln(L)}} + {\rho\left( {L > \mu} \right)}}\end{matrix} \right.} & \left( {{Expression}\mspace{14mu} 4} \right)\end{matrix}$

In the expression, L is the luminance of an image and standardized at areference white level, where V may exceed 1, meaning that thisconversion function also supports luminance greater than the referencewhite, V is a numerical value corresponding to an electric signal, μ isa breakpoint between a gamma curve and a logarithmic curve anddetermines the maximum value of L where V is 1 or less, and α, β, γ, δ,and ρ are each a constant and specific numerical examples thereof areα=4.5, β=0.018, γ=1.099, δ=0.45, and ρ=0.099.

In other words, as represented by Expression 4, the second OETF may bean OETF defined by a linear term of the luminance of video data in athird range of the luminance of the video data, defined by anexponential term of the luminance of the video data in a fourth range ofthe luminance of the video data greater than the third range, anddefined by a logarithmic term of the luminance of the video data in afifth range of the luminance of the video data greater than the fourthrange.

The first OETF may be the function determined according to Expression 5below.[Math. 4]V=L ^(α)  (Expression 5)

In this expression, L is the luminance of an image and standardized as0<L<1 at a reference white level, V is a numerical value correspondingto an electric signal, and a is a constant and a specific numericalexample thereof is α=0.5.

In other words, as represented by Expression 5, the first OETF may be anOETF defined by an exponential term of the luminance of the video data.

The second OETF may be the function determined according to Expression 6below. In this OETF, a conversion function is defined by a logarithmicterm in the range of high luminance.

[Math.  5] $\begin{matrix}{V = \left\{ \begin{matrix}{L^{\alpha}\left( {0 \leq L \leq \mu} \right)} \\{{\eta\;\ln\;(L)} + {\rho\left( {L > \mu} \right)}}\end{matrix} \right.} & \left( {{Expression}\mspace{14mu} 6} \right)\end{matrix}$

In this expression, a is a constant and a specific numerical examplethereof is α=0.5.

In other words, as represented by Expression 6, the second OETF may bean OETF defined by an exponential term of the luminance of video data ina sixth range of the luminance of the video data and defined by alogarithmic term of the luminance of the video data in a seventh rangeof the luminance of the video data greater than the sixth range.

Although the data generation device (the data generation method) and thedata reproduction device (the data reproduction method) according to oneor more aspects are described thus far based on the embodiment, thepresent disclosure is not limited to this embodiment. Variousmodifications of the present embodiment as well as embodiments resultingfrom combinations of structural elements of the different embodimentsthat may be conceived by those skilled in the art may be included withinthe scope of one or more aspects as long as these do not depart from theessence of the present disclosure.

For example, in each embodiment described above, each of the structuralelements may be configured in the form of an exclusive hardware productsuch as a circuit, or may be realized by executing a software programsuitable for each of the structural elements. Each of the structuralelements may be realized by means of a program executing unit, such as acentral processing unit (CPU) and a processor, reading and executing thesoftware program recorded on a recording medium such as a hard disk or asemiconductor memory.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to a data transmission device or adata reproduction device such as a BD device.

What is claimed is:
 1. A data generation method for generating videodata that covers a second luminance dynamic range wider than a firstluminance dynamic range and has reproduction compatibility with a firstdevice that does not support reproduction of video having the secondluminance dynamic range and supports reproduction of video having thefirst luminance dynamic range, the data generation method comprising:generating a video signal to be included in the video data using asecond opto-electrical transfer function (OETF) to be referred to by asecond device when the second device decodes the video data, the seconddevice supporting reproduction of video having the second luminancedynamic range; storing, into video usability information (VUI) in thevideo data, first transfer function information for identifying a firstOETF to be referred to by the first device when the first device decodesthe video data; and storing, into supplemental enhancement information(SEI) in the video data, second transfer function information foridentifying the second OETF.
 2. The data generation method according toclaim 1, further comprising storing, into a descriptor of a multiplexinglayer, hybrid information indicating whether or not the video data isvideo data covering the second luminance dynamic range.
 3. The datageneration method according to claim 1, wherein the first OETF is anOETF defined by a linear term of luminance of the video data in a firstrange of the luminance of the video data and defined by an exponentialterm of the luminance of the video data in a second range of theluminance of the video data, the second range being greater than thefirst range.
 4. The data generation method according to claim 1, whereinthe second OETF is an OETF defined by a linear term of luminance of thevideo data in a third range of the luminance of the video data, definedby an exponential term of the luminance of the video data in a fourthrange of the luminance of the video data, and defined by a logarithmicterm of the luminance of the video data in a fifth range of theluminance of the video data, the fourth range being greater than thethird range, the fifth range being greater than the fourth range.
 5. Thedata generation method according to claim 1, wherein the first OETF isan OETF defined by an exponential term of luminance of the video data.6. The data generation method according to claim 1, wherein the secondOETF is an OETF defined by an exponential term of luminance of the videodata in a sixth range of the luminance of the video data and defined bya logarithmic term of the luminance of the video data in a seventh rangeof the luminance of the video data, the seventh range being greater thanthe sixth range.
 7. The data generation method according to claim 1,wherein the first OETF is an OETF defined in one of BT. 709 and BT.2020, and the second OETF is a hybrid gamma OETF.
 8. The data generationmethod according to claim 1, further comprising storing, into the SEI,dynamic range increase information indicating a difference between aluminance dynamic range of the video data and the first luminancedynamic range.
 9. The data generation method according to claim 1,further comprising storing, into the SEI, maximum average picture levelinformation indicating a highest average luminance value among averageluminance values of all pictures included in a video sequence.
 10. Adata reproduction method for reproducing video data that covers a secondluminance dynamic range wider than a first luminance dynamic range andhas reproduction compatibility with a first device that does not supportreproduction of video having the second luminance dynamic range andsupports reproduction of video having the first luminance dynamic range,the video data including: video usability information (VUI) storingfirst transfer function information for identifying a firstopto-electrical transfer function (OETF) to be referred to by the firstdevice when the first device decodes the video data; and supplementalenhancement information (SEI) storing second transfer functioninformation for identifying a second OETF to be referred to by a seconddevice when the second device decodes the video data, the second devicesupporting reproduction of video having the second luminance dynamicrange, the data reproduction method comprising: obtaining the secondtransfer function information included in the SEI; and reproducing avideo signal included in the video data by referring to the second OETFidentified in the second transfer function information obtained.
 11. Thedata reproduction method according to claim 10, wherein the video datafurther includes hybrid information indicating whether or not the videodata is video data covering the second luminance dynamic range, thehybrid information being stored in a descriptor of a multiplexing layer,and the data reproduction method further comprises: obtaining the hybridinformation from the video data; preparing for switching between thereproduction of the video having the first luminance dynamic range andthe reproduction of the video having the second luminance dynamic range,based on the hybrid information obtained; and switching the reproductionof the video having the first luminance dynamic range and thereproduction of the video having the second luminance dynamic range at atiming of a change in a video sequence.
 12. The data reproduction methodaccording to claim 10, wherein the first OETF is an OETF defined by alinear term of luminance of the video data in a first range of theluminance of the video data and defined by an exponential term of theluminance of the video data in a second range of the luminance of thevideo data, the second range being greater than the first range.
 13. Thedata reproduction method according to claim 10, wherein the second OETFis an OETF defined by a linear term of luminance of the video data in athird range of the luminance of the video data, defined by anexponential term of the luminance of the video data in a fourth range ofthe luminance of the video data, and defined by a logarithmic term ofthe luminance of the video data in a fifth range of the luminance of thevideo data, the fourth range being greater than the third range, thefifth range being greater than the fourth range.
 14. The datareproduction method according to claim 10, wherein the first OETF is anOETF defined by an exponential term of luminance of the video data. 15.The data reproduction method according to claim 10, wherein the secondOETF is an OETF defined by an exponential term of luminance of the videodata in a sixth range of the luminance of the video data and defined bya logarithmic term of the luminance of the video data in a seventh rangeof the luminance of the video data, the seventh range being greater thanthe sixth range.
 16. The data reproduction method according to claim 10,wherein the first OETF is an OETF defined in one of BT. 709 and BT.2020, and the second OETF is a hybrid gamma OETF.
 17. The datareproduction method according to claim 10, further comprising obtaining,from the SEI, dynamic range increase information indicating a differencebetween a luminance dynamic range of the video data and the firstluminance dynamic range.
 18. The data reproduction method according toclaim 10, further comprising obtaining, from the SEI, maximum averagepicture level information indicating a highest average luminance valueamong average luminance values of all pictures included in a videosequence.
 19. A data generation device which generates video data thatcovers a second luminance dynamic range wider than a first luminancedynamic range and has reproduction compatibility with a first devicethat does not support reproduction of video having the second luminancedynamic range and supports reproduction of video having the firstluminance dynamic range, the data generation device comprising: agenerator that generates a video signal to be included in the video datausing a second opto-electrical transfer function (OETF) to be referredto by a second device when the second device decodes the video data, thesecond device supporting reproduction of video having the secondluminance dynamic range; a first storage that stores, into videousability information (VUI) in the video data, first transfer functioninformation for identifying a first OETF to be referred to by the firstdevice when the first device decodes the video data; and a secondstorage that stores, into supplemental enhancement information (SEI) inthe video data, second transfer function information for identifying thesecond OETF.
 20. A data reproduction device which reproduces video datathat covers a second luminance dynamic range wider than a firstluminance dynamic range and has reproduction compatibility with a firstdevice that does not support reproduction of video having the secondluminance dynamic range and supports reproduction of video having thefirst luminance dynamic range, the video data including: video usabilityinformation (VUI) storing first transfer function information foridentifying a first opto-electrical transfer function (OETF) to bereferred to by the first device when the first device decodes the videodata; and supplemental enhancement information (SEI) storing secondtransfer function information for identifying a second OETF to bereferred to by a second device when the second device decodes the videodata, the second device supporting reproduction of video having thesecond luminance dynamic range, the data reproduction device comprising:an obtainer that obtains the second transfer function informationincluded in the SEI; and a reproducer that reproduces a video signalincluded in the video data by referring to the second OETF identified inthe second transfer function information obtained.